[Interest] Draw own QQuickItem using OpenGL together with QQuickApplicationEngine

[Sean Harmer]

Hi,

On Thursday 10 Dec 2015 16:31:38 Axel Jäger wrote:
> Hello Sean,
> thank you for your help. Now I got it working.
> 
> However, I have the feeling that although this works, this is not the proper
> way to do what I want. What do you think? Is this a hack or is it the
> proper way to draw an own item using OpenGL?

What is hackish about it? All we're doing is asking the window to not draw 
it's background color. This is a perfectly valid approach.

Cheers,

Sean

> 
> Best regards,
> 
> Axel
> 
> -----Ursprüngliche Nachricht-----
> Von: Interest [mailto:interest-bounces at qt-project.org] Im Auftrag von Sean
> Harmer
> Gesendet: Sonntag, 6. Dezember 2015 10:46
> An: interest at qt-project.org
> Betreff: Re: [Interest] Draw own QQuickItem using OpenGL together with
> QQuickApplicationEngine
> 
> Hi,
> 
> On 05/12/2015 23:28, Axel Jäger via Interest wrote:
> > Hello,
> > I am trying to start a new application and want to start with the most
> > modern possible codebase so I am looking into different options. The
> > application I want to develop consists of a large OpenGL-View togehter
> > with some slider next to it to change some parameters of the view. I
> > have a large experience in building widget based applications in Qt
> > but just for the fun, I want to go for QML way.
> > 
> > I found this example that shows how to combine OpenGL-Drawing with
> > with
> > QML-Items:
> > 
> > http://doc.qt.io/qt-5/qtquick-scenegraph-openglunderqml-example.html
> > 
> > Then I found the Qt Quick Controls template in QtCreator that uses
> > QQuickApplicationEngine which seems even more sophisticated than just
> > using a QQuickView with a QML-File as a root item.
> > I tried adopting the first example to use QQuickApplicationEngine by
> > changing the main-method according to the template and changed the
> > main.qml to use ApplicationWindow instead of Item as the root object.
> > The effect is that I see all the QML Items in a window but the custom
> > opengl drawing is not displayed. I see from the debugger that the
> > opengl drawing code is executed.
> > 
> > 
> > Attached you will find my modified example. I guess that I just did
> > something very stupid and the viewport of my custom opengl items is
> > something like 0x0.
> > I would be very happy if there was a an example that uses
> > QQuickApplicationEngine to load a qml-file with an ApplicationWindow
> > and that does some OpenGL drawing besides QtQuick based controlls.
> > Any help is greatly appriciated.
> 
> You're almost there. The clue is if you change the rendering to be done as a
> result of the afterRendering() signal instead of beforeRendering() it
> works. So that means the GL code is all fine. So, something must either be
> clearing or drawing on top of your GL rendering.
> 
> It turns out that the ApplicationWindow by default paints itself with the
> widget colour. You can use a style to disable this like so:
> 
> ApplicationWindow {
>      visible: true
>      width: 320
>      height: 480
>      style: ApplicationWindowStyle {
>          background: Item {}
>      }
> 
>      Squircle { ... }
> 
>      ...
> }
> 
> Then it works as expected.
> 
> Cheers,
> 
> Sean
> 
> --
> Dr Sean Harmer | sean.harmer at kdab.com | Managing Director UK KDAB (UK) Ltd,
> a KDAB Group company Tel. +44 (0)1625 809908; Sweden (HQ) +46-563-540090
> Mobile: +44 (0)7545 140604
> KDAB - Qt Experts
> 
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> Interest at qt-project.org
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-- 
Dr Sean Harmer | sean.harmer at kdab.com | Managing Director UK
KDAB (UK) Ltd, a KDAB Group company
Tel. +44 (0)1625 809908; Sweden (HQ) +46-563-540090
Mobile: +44 (0)7545 140604
KDAB - Qt Experts